1. Field of the Invention
The present invention relates to a structure of a digital displacement measuring instrument for measuring displacement of a spindle in an axial direction.
2. Description of Related Art
Conventionally there have been used displacement measuring instruments for measuring dimensions of an object for measurement according to a sliding rate of a spindle. Among the displacement measuring instruments, especially a digital displacement measuring instrument is easy to handle, and can measure dimensions more accurately. When the digital displacement measuring instrument is used in an environment in which water droplets or droplets of other liquids such as grinding oil are frequently sputtering, if the droplets come into inside of the displacement measuring instrument, an encoder may produce improper operating signals to generate an error or a failure. To solve this problem, there has been developed a digital displacement measuring instrument having resistance against water and oil (Refer to, for instance, JP2786801B, FIG. 3).
FIG. 8 shows a micrometer 100B based on the conventional technology. This micrometer 100B has a digital encoder 400 for detecting a sliding rate of a spindle 2. Provided in this encoder 400 are a rotor 401 rotating in association away with rotation of the spindle 2 transmitted thereto, and a stator 402 fixed to a frame body 900 with a prespecified space from the rotor 401. A stator fixing section 403 is fixed to this stator 402, and this stator fixing section 403 is fixed to a holding ring 901 by screwing a screw 903 penetrating a stator mount hole 902 provided on the holding ring 901.
As a waterproofing mechanism for this micrometer 100B, there are a seal member 904 provided between the stator mount hole 902 and the screw 903, and a seal member 905 provided between the holding ring 901 and the frame body 900.
With the micrometer described in the document above, however, it is necessary to provide a stator mount hole 902 for screwing the screw therein on the holding ring 901 to fix the stator 402 more tightly by means of screwing from the outside. It is not desirable to provide a hole on the holding ring 901 exposing to the outside from the view point of a waterproofing structure, and in addition the actions for water proofing processing in the screwing section are very complicated.